1. Field of the Invention
The present invention relates to a process for manufacturing a wiring board and, more particularly, to a process for manufacturing a circuit board in which a first wiring pattern formed on a first surface of a substrate made of resin as a basic material is electrically connected to a second wiring pattern formed on a second surface opposite to the first surface by means of vias penetrating through the substrate.
2. Description of the Related Art
One of the known processes for manufacturing a wiring board on which semiconductor elements, or other electronic elements, is mounted are called a xe2x80x9cdamascenexe2x80x9d method.
An example of such xe2x80x9cdamascenexe2x80x9d method is shown in FIGS. 10(a) to 10(e). FIG. 10(a) is a cross-sectional view of a wiring board 100 on which wiring patterns 140a are formed. The wiring board 100 is made of resin as a basic material. The wiring pattern 140a can be formed by coating photo-resist on the respective surfaces of the resin plate on which copper foils are attached beforehand, light-exposing thereto in accordance with a predetermined pattern for forming the wiring patterns 140a, developing the same to form a resist pattern, and etching the exposed portions of the copper foil using a masking of the resist pattern to remove the exposed area.
The wiring patterns 100a formed on the respective surfaces of the wiring board 100 are electrically connected to each other by means of through holes 120. The through holes 120 are formed by forming via holes by drilling the wiring board 100, and then forming a thin metal film on the inner wall of the via holes by electroless-plating, and then forming a conductor layer on the inner wall of the via holes by electroplating using the thin metal film as a power-supply layer.
In addition, on the respective surfaces 160a and 160b of the wiring board 100 shown in FIG. 10(a) resin layers 160a and 160b are formed by coating the same with a resin, such as a polyimide or an epoxy resin, as shown in FIG. 10(b).
As shown in FIG. 10(c), via recesses 130 and wiring pattern recesses 132 are formed on the resin layers 160a and 160b by irradiating laser light, such as, CO2 laser or excimer laser light.
The wiring board 100 thus having the resin layers 160a and 160b formed with the via recesses 130 and wiring pattern recesses 132 is now processed as follows. As shown in FIG. 10(d), after a metal thin film is formed on the inner wall of the via recesses 130 and wiring pattern recesses 132 and on the surface of the resin layer 160a by electroless-plating of copper or the other, an electro-plating is applied to fill the via recesses 130 and wiring pattern recesses 132 with plated metal 134 using the metal thin film as a power-supply layer. In this case, the surface of the resin layer 160a is also coated with a plated metal 134.
Therefore, the plated metal 134 covering the surface of the resin layer 160a is removed by polishing, as shown in FIG. 10(e), and thus the surface of the resin layer 160a is exposed. By such a polishing the wiring patterns 150a consisting of vias 120 formed with the filled plated metal 134 in the via recesses 130 and plated metal 134 filled in the wiring pattern 132 recesses are exposed on the same surface as the surface of the resin layer 160a, so that the wiring patterns 150a are formed on the surface of the resin layer 160a. 
According to the xe2x80x9cdamascenexe2x80x9d method as mentioned above, very fine and dense wiring patterns can be obtained as compared with a conventional wiring board which is made by a xe2x80x9csub-tractivexe2x80x9d method or a xe2x80x9csemi-additivexe2x80x9d method as known in the prior art.
However, the wiring patterns formed on the respective surfaces of the wiring board 100 are electrically connected with each other by means of through holes 120. Since the wiring pattern and through holes 120 are formed respectively by the separate processes, it is difficult to reduce the production cost of the wiring board 100.
Also, since the via recesses 130 and wiring pattern recesses 132 of the resin layers 160a and 160 are formed by irradiating laser light, such as CO2 laser or excimer laser light, a facility for irradiating laser light is necessary. Also, since the depth of the via recesses 130 is different from that of the wiring pattern recesses 132, it is necessary to precisely control the intense or irradiation time of laser beam. Thus, the production cost of the obtained wiring board is high.
An object of the present invention is to provide a process for manufacturing a wiring board capable of easily forming via recesses for filling with plating metal and of reducing the production cost of the wiring board.
According to the present invention, there is provided a process for manufacturing a wiring board, said process comprising the following steps of: making a resin plate having wiring pattern recesses and via through holes; coating all of the surfaces of the resin plate including inner walls of said wiring pattern recesses and via through holes with a metal film; applying an electro-plating using said metal film as a power-supply layer to fill a plated metal into said wiring pattern recesses and via through holes; and removing said metal film formed on said resin plate except for the inner walls of said wiring pattern recesses and via through holes, so that wiring pattern and vias are exposed on a surface the same as that of said resin plate.
The resin plate is formed by a press-forming process. Otherwise, the resin plate can be formed by an injection molding process.
The above mentioned process further comprises the following steps of: forming pads on one of surfaces of the wiring board to which external connecting terminals are to be attached.
The above mentioned process further comprises the following steps of: using said wiring board as a core substrate; and forming wiring patterns on the respective surface of the core substrate by means of resin layers to obtain a multi-layer wiring board.
According to another aspect of the present invention, there is provided a process for manufacturing a multi-layer wiring board, said process comprising:
(a) manufacturing a core substrate comprising the steps of: making a resin plate having wiring pattern recesses and via through holes; coating all of the surfaces of the resin plate including inner walls of said wiring pattern recesses and via through holes with a metal film; applying an electro-plating using said metal film as a power supply layer to fill a plated metal into said wiring pattern recesses and via through holes; and removing said metal film formed on said resin plate except for the inner walls of said wiring pattern recesses and via through holes, so that wiring pattern and vias are exposed on a surface same as that of said resin plate; and
(b) forming resin layers on respective surfaces of said core substrate so that said resin layers includes wiring pattern recesses and via through holes;
(c) coating all of surfaces of said resin layers including inner walls of said wiring pattern recesses and via through holes with a metal film;
(d) applying an electro-plating using said metal film as a power supply layer to fill a plated metal into said wiring pattern recesses and via through holes; and
(e) removing said metal film attached to said resin layer except for the inner walls of said wiring pattern recesses and via through holes, so that wiring pattern and vias are exposed on a surface same as that of said resin plate.